On Friday, more than 1,000 head teachers marched on Downing Street to protest against ‘dangerous’ cuts to budgets.

Judy Shaw, vice-president of the National Association of Head Teachers, has said that things are at such a critical point, her primary school has no more than £80 left in its budget by the end of the academic year.

Another head teacher – this one at a primary school in Theresa May’s constituency – has written to parents asking them to pay for toilet paper.

So, is it really the case then, as any neutral observer might conclude, that budgets have been savagely cut by this heartless Tory government?

In fact, the opposite is true.

The last school year, for example, saw the Government devote an enormous £39 billion to education for five to 16 year-olds in England, up from £37 billion the year before.

This is the highest amount ever spent on schools.

Protesters claim the figure is misleading because it doesn’t take into account rising pupil numbers and inflation. But the Institute for Fiscal Studies (IFS), a politically independent economic research body, insists that spending on schools has doubled in the past two decades, even allowing for those factors.

According to the IFS, in fact, the average amount received per pupil by primary schools increased by a whopping 114 per cent in real terms between 1997 and 2015. Secondary schools, too, have been treated well, enjoying a 90 per cent rise in real terms over the same period.

If Mrs Shaw’s school has a mere £80 left in its coffers, it is unlikely that the fault lies with the Government. And if, like me, you’re wondering where all that extra money has gone, here’s a clue: 1,300 head teachers in England are paid more than £100,000, and 600 are paid more than £110,000.

If they’re really so concerned about money for toilet paper, maybe they should pay themselves a bit less.

What, then, is really going on?

The truth is that many of the head teachers thronging Whitehall on Friday and waving placards – instead of being in their schools, where they should have been – are politically motivated militants determined to see Jeremy Corbyn installed as Prime Minister.

At the last General Election, only eight per cent of teachers voted Conservative, compared to 68 per cent who voted Labour, and my worry is that they’re bringing this political bias into the classroom.

That was certainly the impression many voters were given last year when they turned up at schools being used as polling stations to be greeted with classroom windows plastered with anti-Conservative propaganda.

The National Union of Teachers spent more money on political campaigning in the run-up to the General Election than either Ukip or the Green Party.

The Department for Education is so concerned about this Left-wing bias it felt compelled to issue an official warning earlier this month, reminding schools that the promotion of one particular viewpoint by teachers is against the law.

All staff have a responsibility to ensure that they act appropriately in terms of their behaviour, the views they express (in particular political views) and the use of school resources at all times, and should not use school resources for party political purposes,’ the warning read.

That bit about ‘school resources’ should have been underlined in red pen.

Last year, the same school teachers who organised Friday’s demo dispatched letters to 2.5 million homes warning of the terrible damage being inflicted on children’s education by brutal Tory ‘cuts’. The letters might as well have been Labour Party election leaflets.

As the co-founder of four free schools, I’ve always taken pains to ensure our students are exposed to a range of different views, inviting guests to visit from both sides of the political divide.

We’ve had David Cameron and Michael Gove come in and talk to the children; Labour peer Lord Adonis and the local Labour MP Andrew Slaughter have done the same.

But I also spend a fair amount of time visiting schools myself, and the impression I get is not encouraging: in nearly every case it seems the students have never encountered a Conservative speaker before.

When I tell audiences that two million more children are now being taught in schools ranked ‘good’ or ‘outstanding’ than they were under Labour; or that more jobs have been created in the UK than in the whole of the EU since 2010; or that the deficit has come down by more than two-thirds thanks to the financial prudence of successive Conservative Chancellors, they look at me with open-mouthed astonishment.

It’s as if they’ve never heard these facts before.

At the conclusion of my talks, the children often find it difficult to get a word in edgeways because the teachers are so eager to challenge me.

And far from disguising their political leanings or making an effort to be even-handed, the staff make it crystal-clear that they are Labour supporters.

I half expect them to whip the children up into a chant of ‘Oh, Jeremy Corbyn’.

We saw evidence of this bias at last week’s Labour Party conference.

A young teaching assistant named Sion Rickard was greeted with rapturous applause when he said: ‘If we give children a proper education, we’ll empty our prisons, we’ll have much less problems with the NHS, social issues, we’ll probably not have any Tories because we will have brought up our kids properly.’

Not have any Tories? Just take a second to digest that. A teacher at a state school, whose salary is paid by the taxpayer, claims that any student who supports the Conservatives has not received a ‘proper education’.

The following day, a party official assured Mr Rickard that Labour was 100 per cent behind everything he’d said.

‘Please don’t lose faith,’ she urged – and, once again, the delegates leapt to their feet and applauded.

Perhaps it’s no wonder that Labour is in favour of the political indoctrination of schoolchildren, because as a tactic for winning elections it’s working.

Last year, as many as 62 per cent of 18 to 24-year-olds voted Labour, compared to only 27 per cent who voted Conservative.

You might think this is nothing new – that young people have always been more likely to identify with Labour.

Yet the divide is growing, and rapidly: at the 2010 General Election, for example, the vote was almost neck and neck, with 31 per cent of 18 to 24-year-olds voting Labour compared to 30 per cent who voted Conservative.

This leftward slide among young voters has coincided with a similar drift among teachers.

In 2010, a pre-Election poll found that 25 per cent of teachers intended to vote Labour and 18 per cent for the Conservatives. Not neck and neck, but a great deal closer than the alarming 68 per cent to eight per cent split today.

It’s hardly surprising, then, that the Labour Party is campaigning to lower the voting age to 16 – and I dare say the next step will be to lower it to 14.

This brainwashing of young people by Left-wing teachers has got to stop.

The Department for Education needs to do more than issue warnings. And it’s time to start enforcing the law before the dream of Labour teachers such as Sion Rickard is realised – and the percentage of school leavers with the ability to think for themselves is actually reduced to zero.